Crystalline glucans

Naturally, very long T,c values are expected for solids as viewed from the expected correlation time at the low temperature side of the T c minimum (0.1-0.2 s) as shown in Figure 1. Indeed, their values turns out to be the order of 10-30 s for carbon sites in the absence of internal fluctuations as in polysaccharides such as (1 — 3)-p-D-glucan and (1 —> 3)-p-D-xylan,46 8 fibrous proteins such as collagen49 and silk fibroin,50 free and metal-complexed ionophores,51 or in some instances up to 1000 s as in crystalline polyethylene.52... 

Cellobiohydrolase I (CBH I, 1,4-jS-D-glucan-cellobiohydrolase, E.C. 3.2.1.91) is the main protein (ca. 60%) of the cellulase complex produced by T. reesei strains. CBH I hydrolyses crystalline cellulose, acid swollen cellulose and 4-methylumbelliferyl-cellodex-trins by cleaving off the terminal cellobiose unit from the non reducing end of the chain. It operates with retention of configuration in the reaction products 19,20. The abundance of this enzyme and its stability has facihtated its purification to homogeneity... 

Cyclodextrins (CDs) were first observed by Villiers (i) nearly a century ago. First thought to be a mysterious crystalline form of starch, the structure and chemistry of these unique cyclic glucan oligosaccharides have been elucidated through the contributions of Schardinger, Freudenburg, Cramer and French (2). 

Submicrofibril and triple-stranded left-hand helical microfibrils are found in tobacco primary cell wall and bacterial A. xylinum cellulose. We suspect from our results and the literature survey outlined in reference (1) that the triple stranded structures are prominent in the primary plant cell wall. The highly crystalline cellulose of plant and algae secondary cell wall appears by X-ray fiber diffraction (18,19) and TEM lattice imaging (20-23) to be largely crystalline arrays of planar straight chains of (l-4)-/3-D-glucan chains. 

Varghese and coworkers have identified the active site nucleophiles of two crystalline ) -D-glucan endohydrolases from germinating barley [70]. In more recent work, Hej and coworkers were able to introduce 2,3-epoxypropyl- -laminaribioside 8 (n = 1) into the active site of the crystalline l,3-/3-D-glucanase from barley [71]. A subsequent X-ray crystallographic investigation gave invaluable information about the active site of this enzyme and the point of attachment between enzyme and inhibitor was confirmed. 

Vacuum-ultraviolet, circular dichroism (v.u.c.d.) measurements have been made on films and solutions of linear D-glucan in a study of the conformation of dextran and its oligomers.123 Film formation of the linear dextran was accompanied by crystallization, and the v.u.c.d. band was observed at 165 nm, in contrast to nonlinear dextran films displaying a band at 177 nm. The difference was ascribed to hydrogen bonding of the ring-oxygen atom in the crystalline state. 

Jelsma, J. Kreger, D. R. Polymorphism in crystalline (l-3)-fungal cell-walls. Carbohydrate Res.. 1979, li, 51-64. 

As the X-ray diffraction diagrams of an oriented gel (Fig. 6) are poorly crystalline, it has been useful to conduct X-ray crystal structure analyses of oligomer of 3-(l->-3)-D-glucan. The molecular structures of laminarabiose and its acetyl derivative have been determined. 

Amylose, a linear, high molecular weight (l- -U)-a-D-glucan, is one of the principal polysaccharides of starch. Because of the longstanding utility of starch as a raw material, and its widespread botanical availability, its structure and properties have been studied for centuries. Since the more recent realization that almost all varieties of starch are composed of two polysaccharides - the linear amylose and the branched amylopectin - a significant share of interest has shifted to the study of these components. Of particular interest has been the observation that both components occur naturally in crystalline form in the starch granule. 

Initially, the action of maltose (3-amylase on amylose gave complete conversion into maltose,235 and amylose was considered to be a completely linear a-(l—>4) glucan. However, when highly purified crystalline sweet potato (3-amylase was used, the... 

All wheat starches give the same A-type crystal pattern, but their degree of crystallinity is inversely proportional to amylose content. In addition, the intensity of one reflection of an amylose-lipid complex at 2 20-23° (d 4.4A) increases proportionally to the amylose level.265,271,281,284,289 The lipid content of waxy wheat starch is much lower (0.02-0.17%) than that in non-waxy wheat starch (0.6-0.7%).286,291 However, the crude fat content of waxy wheat flour is elevated by 20-40% (3-glucan and pentosan are increased by 30%.291,292 The degree of crystallinity of waxy wheat starch is reported to be 18-21% versus 13-16% for the wild type.284,289 Increases of 35% for waxy wheat starch, 23-28% for double nulls, 20-23% for single nulls and 22% for the wild type have also been reported.271... 

Polymerization of the D-glucan chains occurs by way of a multi-subunit, enzyme complex embedded in the plasma membrane an almost simultaneous association, by means of hydrogen bonds, of the newly formed chains results in formation of partially crystalline microfibrils. This mechanism of polymerization and crystallization results in the creation of microfibrils whose chains are oriented parallel (cellulose I). In A. xylinum, the complex is apparently immobile, but, in cells in which cellulose is deposited as a cell-wall constituent, it seems probable that the force generated by polymerization of the relatively rigid microfibrils propels the complex through the fluid-mosaic membrane. The direction of motion may be guided through the influence of microtubules. 

Cel6A (CBH II) -20% of total secreted protein Various isoenzymes (pi 5.1-6.3 pi 5.9+) (difficult to purify) 53kDa+ pi 5.9+ CBD (N-terminal) From non-reducing end Single displacement— Inversion of the anomeric carbon Attacks amorphous and crystalline cellulose Active on P-glucan... 

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